In the past dentists used primarily gold or silver alloys to fill or otherwise repair teeth. Other less expensive restorative materials are now being used as substitutes for silver and gold. These newer restorative materials also have the advantages of matching the color of a patient's teeth and being highly durable. Typically the newer materials are a composite of an organic bonding agent and an inorganic filler material. The composite material is applied to the patient's tooth in thin layers and then cured by applying light of a proper frequency. The optimum light frequency range for rapid and uniform curing of the material depends on the specific composition of the material.
Known apparatus for curing dental repair composites typically include a light bulb disposed within a housing and a switch for interconnecting the light bulb with standard alternating current from a wall socket. A flexible cord composed of fiber optic strands directs the light from the bulb to the patient's tooth.
Some known types of light curing units produce light in a wide range of frequencies far beyond that required for rapidly and completely curing the specific restorative materials being used. The additional frequencies of light can actually hinder the effective grafting together of the polymer and monomer which compose the bonding agent of the composite.
Higher frequencies of ultraviolet light, especially below 300 nanometers, cause radical cross-linking of the organic molecules of the restorative composite resulting in instability of the composite. Consequently, the composite breaks down over time. Also, clinical studies have shown that higher frequency ultraviolet rays can cause damage to gum tissue. Thus, it is important that these frequencies of ultraviolet light produced by light curing units be attenuated.
Wavelengths of light not absorbed during the curing of restorative composites, especially those above 700 nanometers, generate substantial amounts of heat. This heat can cause a thin outer shell to form on the composite material so that the oxides created during the curing process are not able to flash off of the composite material. As a result, the interior portions of the composite material may not fully cure, resulting in premature failure of the restorative material.
Also, the light produced by known light generating units often is not intense enough to penetrate very deeply into composite materials. As a consequence, these materials must be applied in very thin layers, thereby increasing the time required to complete a filling or perform the dental work. The lack of light intensity in part may be due to the inefficiency of the filter or other means, if any, used to control the frequency of the light produced by the unit.
Thus, it is a primary object of the present invention to overcome the shortcomings of known curing light generating systems discussed above. The present invention provides a method for determining the proper frequency range of light for optimally curing organic restorative dentistry composites. Further, the present invention provides an apparatus which is capable of producing high intensity light in the precise frequency range which has been found by the present method to cure the particular composite material utilized to repair the tooth while attenuating or minimizing harmful or unwanted frequencies of light.